In
computer networking
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
, packet delay variation (PDV) is the difference in
end-to-end one-way delay
End-to-end delay or one-way delay (OWD) refers to the time taken for a Packet (information technology), packet to be transmitted across a computer network, network from source to destination. It is a common term in IP network monitoring, and differ ...
between selected packets in a
flow with any
lost packets being ignored.
[RFC 3393] The effect is sometimes referred to as packet jitter, although the definition is an imprecise fit.
Terminology
The term PDV is defined in ITU-T Recommendation Y.1540
Internet protocol data communication service - IP packet transfer and availability performance parameters section 6.2.
In
computer networking
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
, although not in
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
, usage of the term
jitter may cause confusion. From RFC 3393 (section 1.1):
The variation in packet delay is sometimes called "jitter". This term, however, causes confusion because it is used in different ways by different groups of people. ... In this document we will avoid the term "jitter" whenever possible and stick to delay variation which is more precise.
Measurement of packet delay variation
The means of packet selection for measurement is not specified in RFC 3393, but could, for example, be the packets which had the largest variation in delay in a selected time period.
The delay is specified from the start of the packet being transmitted at the source to the start of the packet being received at the destination. A component of the delay which does not vary from packet to packet can be ignored, hence if the packet sizes are the same and packets always take the same time to be processed at the destination then the packet arrival time at the destination could be used instead of the time the end of the packet is received.
''Instantaneous packet delay variation'' is the difference between successive packets—here RFC 3393 does specify the selection criteria—and this is usually what is loosely termed "jitter", although jitter is also sometimes the term used for the
variance
In probability theory and statistics, variance is the expectation of the squared deviation of a random variable from its population mean or sample mean. Variance is a measure of dispersion, meaning it is a measure of how far a set of numbe ...
of the packet delay. As an example, say packets are transmitted every 20 ms. If the 2nd packet is received 30 ms after the 1st packet, IPDV = −10 ms. This is referred to as ''dispersion''. If the 2nd packet is received 10 ms after the 1st packet, IPDV = +10 ms. This is referred to as ''clumping''.
PDV diagrams
It is also possible to visualize (I)PDV measurements, which makes interpreting and understanding the network easier, or (for bigger datasets) possible at all.
One possible diagram type are simple "Point cloud" diagrams in which the x-axis represents the packet number and the y-axis contains the corresponding (I)PDV values, one dot for each measurement.
Another type are distribution histograms which are more useful for bigger datasets or even comparisons of different paths or technologies.
Limiting PDV or its effects
For interactive real-time applications, e.g.,
voice over IP
Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
(VoIP), PDV can be a serious issue and hence VoIP transmissions may need
quality of service
Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...
-enabled networks to provide a high quality channel.
The effects of PDV in
multimedia
Multimedia is a form of communication that uses a combination of different content forms such as text, audio, images, animations, or video into a single interactive presentation, in contrast to tradit ...
streams can be mitigated by a properly sized buffer at the receiver. As long as the bandwidth can support the stream, and the buffer size is sufficient, buffering only causes a detectable delay before the start of media playback.
See also
*
Latency (engineering)
Latency, from a general point of view, is a time delay between the cause and the effect of some physical change in the system being observed. Lag, as it is known in gaming circles, refers to the latency between the input to a simulation and ...
References
Network architecture
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